The macrolide FK506, which is of the formula: ##STR1## is manufactured by Fujisawa Pharmaceutical Company Limited, and is a known immunosuppressant. It is a member of class of immunophilins described by Schreiber, S. L. in Science (1991) 251:283-287. Other members of this class include rapamycin, cyclosporin A, and an additional macrolide designated 506BD. However, the present applicant is unaware of any suggestion that FK506, which is also known to be a proline isomerase (or rotamase) inhibitor, or the other compounds described in this article would have antiviral activity. Unexpectedly, FK506 was found to be capable of inhibiting hepatitis Delta virus (HDV) replication.
U.S. Pat. No. 5,196,437 describes the ability of compounds related to FK506 to regenerate liver which has been negatively affected by hepatitis B and non A/non B. However, this appears to be unconnected with any direct effect on the virus.